EXTERNAL STRUCTURE 



309 



and South America. They are of ancient origin, a fossil genus, 

 Graeophonus, of the Tarantulidae (Phrynidae, see p. 3 1 2), occurring 

 in the Carboniferous strata in North America. They live under 

 stones and bark, and in eaves, where, v?hen disturbed, they seek 

 safety in crannies in the rock. 



Little is known of their habits, but they are believed to feed 

 chietly upon insects. The female Tarantula carries the developing 

 eggs, somewhat after the manner of the Chernetidea (see p. 434), 

 in a bag beneath the abdomen, the under surface of which 

 becomes concave and dome-like during the period of gestation.^ 



External Structure. — The external features which the 

 members of this Order have in common are the segmented 

 pediculate abdomen (9 to 12 segments), 

 the two -jointed non-chelate chelicerae, 

 the antenniform first pair of legs, and 

 the presence of two pairs of lung-book 

 stigmata beneath the abdomen. The 

 constituent families differ so much in 

 outward form that they must be dealt 

 with separately. 



The Thelyphonidae or " Whip Scor- 

 pions " (see p. 312) have a long-oval cara- 

 pace bearing well-developed eyes, two in 

 front, and a group of three or five on 

 either side some distance behind. The 

 pedipalpi are chelate, and have their basal 

 joints fused beneath the mouth, being thus 

 incapable of any masticating motion. 



The first legs are six -jointed, and fiq. 171. 

 have multi-articulate tarsi ; the others 

 are seven-jointed, and their tarsi, in some 

 species at least, are tri-articulate. The 

 abdomen consists of two portions, a wide 

 nine -jointed pre -abdomen and a short 

 narrow three -jointed post -abdomen, to 

 which a filiform tail is articulated. Beneath the cephalothorax, 

 between the coxae of the legs, is a distinct sternal plate in two 

 portions (Fig. 171). The first abdominal ventral plate is largely 

 developed, and covers two segments. Behind it are the median 



' Laurie, J. Linn. Soc. Zool. xxv. , 1894, p. 00. 



Thelyxihonus, dia- 

 grammatio ventral view ; 

 about natural size. c, 

 Coxal joint of pedipalp ; 

 g, generative opening ; p, 

 pedipalp ; sp, spiracles ; 

 st, sternal plates ; 1, 2, 3, 

 4, ambulatory legs. (After 

 Pickard-Cambridge. ) 



